The present invention relates to a method of cast molding a surgical implant produced from two or more dissimilar materials, implants so produced and molds useful therefor. More particularly, the present invention relates to a method of cast molding intraocular lenses produced from two or more dissimilar materials using disposable plastic molds.
The use of intraocular lenses (IOLs) to improve vision through the replacement of damaged or diseased natural lenses or to work in conjunction with a natural lens has obtained wide acceptance since the early 1980s. Accordingly, a wide variety of IOLs has been developed for surgical implantation into the posterior and/or anterior chamber of an eye. Commercially available IOLs generally comprise an optic portion and one or more haptic elements or plates to maintain proper positioning of the optic portion within the eye. The optic portions of such IOLs are commonly manufactured from relatively hard or rigid materials such as, for example, polymethylmethacrylate (PMMA), or from relatively soft, resilient polymeric materials such as, for example, hydrogels, acrylics or silicones. More resilient polymeric materials are advantageous in the production of IOLs in that such materials are deformable and foldable to allow for implantation of the IOL through a smaller incision than that possible if implanting a more rigid IOL.
To manufacture a biocompatible IOL using known molding techniques, a polished stainless steel mold, having a mold cavity formed in a shape to achieve the desired refraction of light for the particular material utilized, is first selected. In the case of silicone for example, the uncured silicone polymer is introduced into the mold cavity and then cured. Several methods of molding IOLs are known such as injection molding, liquid injection molding, compression molding and transfer molding.
Several significant problems have been associated with known IOL molding techniques. The first problem is that current molding processes are labor intensive. Many elastomers used to mold IOLs, such as for example silicone elastomers, often times leave a residue in the stainless steel molds. Due to this residue, the molds must be cleaned between each molding cycle. In addition to being labor intensive, the cleaning requirements result in significant downtime for the equipment, which further increases production costs. A second problem associated with current known molding techniques is that of frequent tool damage and wear due to the repeated cleanings. Accordingly, molds must be replaced often resulting in increased production costs. A third problem associated with such molding techniques is one of quality control with respect to the molded lenses. Intraocular implants such as IOLs must have smooth polished edges for implantation within an eye. Improperly finished edges on implants may result in damage to interior structures of the eye. In the case of improperly finished edges on IOLs, abrasions of the iris and tearing of the trabecular meshwork may result. Unfortunately, steel molds typically leave minute gaps between mold halves during the molding operation due to construction tolerances. Consequently, material flows out through the gaps during the molding of the IOL resulting in a phenomenon known as xe2x80x9cflashxe2x80x9d. Flash is unwanted material attached at the mold parting line on the molded implant. This flash material must be ground and/or polished off the implant, which is again labor intensive and increases production costs.
The present invention is a process for cast molding surgical implants, such as but not limited to corneal inlays, shunts and intraocular lenses (IOLs), but most preferably IOLs, wherein in the case of IOLs, the optic portion and haptic elements are produced using two or more dissimilar biocompatible materials. However, if desired, the subject molds and molding techniques are likewise useful in the manufacture of surgical implants such as in the case of IOLs having an optic portion and haptic elements produced using the same or similar biocompatible materials. The present cast molding process avoids the problems noted with regard to known molding techniques through the use of disposable plastic molds, which are less expensive and less labor intensive to make and use.
The cast molding process of the present invention utilizes a multi-part, but preferably in the case of more customary IOLs a four-part, disposable plastic mold system. The first mold part of the subject mold system is a female base mold having a positioning wall formed along the periphery of an interior surface thereof and a molding surface on the interior surface. The molding surface is comprised of a center cavity used to form one surface of an IOL optic portion, one or more but preferably two junction cavities and two or more haptic element cavities. The center cavity is in fluid connection with each junction cavity. Also, each haptic element cavity is in fluid connection with at least one junction cavity.
The second mold part of the subject mold system is a center male mold having a molding surface on an interior surface comprised of an optic cavity used to form the second surface of the IOL optic portion. The center male mold is sized to be fully received within the positioning walls of the female base mold and may be shaped to ensure axial and rotational alignment.
The third and fourth mold parts of the subject mold system are haptic molds. Each haptic mold likewise has a molding surface on an interior surface comprised of one or more junction cavities and at least one haptic element cavity. When the haptic molds are placed in an interlocked relationship with center male mold, junction cavities and haptic element cavities are in fluid connection with optic cavity. Haptic molds are also male molds sized to be fully received within the positioning walls of the female base mold and preferably shaped to ensure axial and rotational alignment. Each haptic mold is also formed to have material guides or ports extending from the haptic element cavity and/or junction cavity through to the exterior surface of the mold. Optionally, center male mold and haptic molds may be formed as a unitary mold.
The subject preferably four-part mold is used to cast mold a surgical implant, preferably an IOL, using two or more dissimilar biocompatible materials. An IOL having an optic portion of one preferably more resilient biocompatible material and haptic elements of a dissimilar preferably more rigid biocompatible material is produced by filling the base mold center cavity with the desired more resilient IOL optic material. The center male mold is then inserted into the female base mold allowing excess molding material to pass into one or more overflow reservoirs. During this process, some molding material flows into fluidly connected junction cavities so as to only partially fill the same. Shields are then positioned over the partially filled junction cavities and the molding material in the center cavity is polymerized using methods of polymerization known to those skilled in the art. Due to shielding, or any suitable method of protection, the molding material in the junction cavities is not polymerized. After removing the shields, the haptic molds are then inserted into the female base mold and a second dissimilar relatively rigid biocompatible molding material is provided through the material guides or ports to completely fill the junction cavities and the haptic element cavities. The remaining unpolymerized first molding material and the second molding material are then polymerized using methods of polymerization known to those skilled in the art. Following polymerization, all three male molds are removed from the female mold. The IOL is removed from the female mold through the use of solvents or vibration.
Accordingly, it is an object of the present invention to provide a cast molding system to produce IOLs having an optic portion and haptic elements produced from dissimilar biocompatible materials.
Another object of the present invention is to provide a method for cast molding IOLs having an optic portion and haptic elements produced from dissimilar materials which is less labor intensive.
Another object of the present invention is to provide a method for cast molding IOLs having an optic portion and haptic elements produced from dissimilar materials with lower production costs.
Another object of the present invention is to provide molds for cast molding IOLs having an optic portion and haptic elements produced from dissimilar materials.
Still another object of the present invention is to provide a method for cast molding IOLs having an optic portion and haptic elements produced from dissimilar materials suitable for high volume production.